1. Field of the Invention
This invention relates to a semiconductor device in which heat is radiated from both sides of a semiconductor chip accommodated therein.
2. Description of the Related Art
For example, JP-A-6-291223 discloses a semiconductor device in which heat is radiated from both sides of a semiconductor chip. FIGS. 1A to 1C show this semiconductor device. As shown in the figures, a pair of radiation members J2, J3 sandwich several semiconductor chips J1, and are thermally and electrically connected to the semiconductor chips J1. The several semiconductor chips J1 arranged on a plane and the radiation members J2, J3 are sealed with resin J5.
Each of the radiation members J2, J3 serves as an electrode, and has a surface exposed from the resin J5 at an opposite side of the face contacting the semiconductor chips J1. Each of the radiation members J2, J3 performs radiation of heat by making the exposed surface contact a contact body (not shown) that can exhibit a radiation action. A control terminal J4 connected with a control electrode of the semiconductor chips J1 protrudes to an outside from the resin J5.
Used as the radiation members J2, J3 is W (tungsten) or Mo (molybdenum) having a thermal expansion coefficient approximate to that of the semiconductor chips J1. The radiation member J2 that is connected to the surfaces of the semiconductor chips J1 on which the control electrode is formed is an emitter electrode, and the radiation member J3 that is connected to the surfaces of the semiconductor chips J1 at an opposite side of the control electrode is a collector electrode.
Besides, several solder bumps J7 protrudes from an insulating plate J6 that has a through hole at a center thereof in which the radiation member J2 penetrates as the emitter electrode. The solder bumps J7 are bonded to bonding pads existing in unit patterns of the respective semiconductor chips J1 disposed on the radiation member J3 as the collector electrode.
When the radiation members J2, J3 serving also as electrodes are made of metallic material such as W or Mo having linear thermal expansion coefficient approximate to that of the semiconductor chips J1 made of Si (silicon), these metallic materials are, in electrical conductivity about one third of that of Cu (copper) or Al (aluminum), and in thermal conductivity about one third to two third thereof. Thus, in the present circumstances involving an increased requirement for flowing a large current in the semiconductor chip, using W or Mo as a member that serves as a radiation member and an electrode simultaneously causes many problems.
Also, in general, a larger chip is required to accommodate a larger current. However, there are many technological problems to increase the chip size, and it is easier to manufacture plural smaller chips and accommodate them into one package.
In the technique disclosed in the publication describe above, the several semiconductor chips J1 are formed in the semiconductor device. However, as shown in FIG. 1A, because the radiation member J2 has a simple rectangular shape, and is provided at the center of the device, disposal of different semiconductor chips in one device is limited. That is, when the semiconductor chips are different from one another in, for example, thickness, it is difficult for the one emitter electrode having a simple shape to be connected to all of the different semiconductor chips.
The present invention has been made in view of the above problem. An object of the present invention is to improve a radiation property and an electrical conductivity of a semiconductor device including radiation members that are thermally and electrically connected to both surfaces of a semiconductor chip therein. Another object of the present invention is to provide a semiconductor device easily accommodating several different semiconductor chips therein.
For example, according to one aspect of the present invention, in a semiconductor device in which a semiconductor chip is thermally and electrically connected to first and second radiation members therebetween, the first and second radiation members are made of a metallic material that is superior to tungsten and molybdenum in at least one of an electrical conductivity and a thermal conductivity. Accordingly, the radiation property and the electrical conductivity of the semiconductor device can be improved.
According to another aspect of the present invention, in a semiconductor device in which first and second semiconductor chips are thermally and electrically connected to first and second radiation members therebetween, the first radiation member has first and second protruding portions protruding toward the first and second semiconductor chips, and first and second front end portions of the first and second protruding portions are thermally and electrically connected to the first and second semiconductor chips through a bonding member.
In this case, even when the first and second semiconductor chips are different from each other in thickness, the first and second radiation members can be provided with first and second radiation surfaces approximately parallel to each other by controlling protruding amounts of the first and second protruding portions.
According to still another aspect of the present invention, in a semiconductor device in which a semiconductor chip is disposed between a first conductive member and a second conductive member, the first conductive member is further bonded to a third conductive member at an opposite side of the semiconductor chip so that a bonding area between the first conductive member and the third conductive member is smaller than that between the first conductive member and the semiconductor chip. Accordingly, stress concentration on the first conductive member can be suppressed to prevent occurrence of cracks. This results in improved radiation property and electrical conductivity of the semiconductor device.